Force of Friction

What is Friction?

FRICTION- It is a force that resists the relative motion of surfaces.



What is Friction?
The force, which opposes the relative motion between two surfaces in contact is known as friction. It occurs due to surface irregularities of the two objects in contact.
What are Surface Irregularities?
This unevenness of the surface is called surface irregularities or roughness.

  • All types of surfaces like solid, liquid, and air offer the force of friction.
  • This force of friction always opposes the applied force.
  • When two objects with their surfaces in contact rub against each other, they cause friction
  • Friction is the force opposite to the direction of motion.


  • Friction is the force that acts when one object tries to move or slide over the surface of another object.
  • It can be defined as the resistance of motion when one objects rub against other.
  • Friction works against the motion and acts in the opposite direction. However, friction does not always oppose the motion, it also helps in motion.
  • The S.I unit in which Frictional Force is measured in Newton.


  • Friction between the tyres of vehicles and the road. A moving tyre on the ground stops after covering a certain distance because the surface of the ground offers opposite direction friction to the surface of the wheel in motion.
  • Gently pushing a book on a table. It stops after moving some distance because of friction between the surfaces of the book and table.
  • Writing on paper using a pencil. Friction between the graphite in a pencil and a sheet of paper leaves a mark on the paper. Same there is a Friction between pen and book.
  • Warming hands in winter. As friction produces heat you can warm your hands in winter by rubbing them against each other. So heat from friction can be useful.
  • Gymnasts apply some coarse substances on their hands to increase friction for better grip
  • To make the box move, we have to apply a force to overcome the force of friction.

Cause of Friction

  • The root cause of friction is the irregularities or rough edges that are ridges and grooves present on the two surfaces which are in contact. Due to this they get interlocked with each other and cause friction.
  • Even smooth surfaces like tiles in houses, offices, schools have a large number of irregularities when seen under a microscope.

Why is it difficult to walk on a smooth or wet floor?
Due to less friction between our foot and floor. As the interlocked irregularities possess a layer of water which decreases friction.
What Causes Friction?
Friction exists between two surfaces due to abnormalities on the surfaces of the objects in contact, as well as the interlocking of the two surfaces' micro-level imperfections. So, this force is caused by molecular adhesion, surface roughness, plowing effect, and deformations.